An odd number of inverters are connected and form a closed circuit so as to form an oscillator. This circuit has been publicly known as a ring oscillator.
Japanese Laid-open Patent Publication No. 2010-50591 discloses a ring oscillator which is capable of generating higher frequencies.
The ring oscillator disclosed in the Japanese Laid-open Patent Publication No. 2010-50591 comprises: a square-shaped main loop circuit including four inverters (an even number of inverters); and a plurality of triangle-shaped loop circuits, each of which includes three inverters (an odd number of inverters) and which act as energizing circuits.
Further, Japanese Laid-open Patent Publication No. 2011-19053 discloses an oscillator comprising: a plurality of main rings, in each of which three inverters are annularly connected; a phase connection ring, in which a plurality of inverters are annularly connected; first connection nodes being respectively provided to the main rings, the first connection nodes of the main rings being respectively connected with different second connection nodes of the phase connection ring; and resistances acting as second phase connection elements, which connect the second connection nodes of the phase connection ring with each other.
The above described conventional oscillators oscillate mere pulse waves. The inventor of the present invention has studied so as to generate a step-like pulse, which includes at least two rising edges and two trailing edges. For example, a step-like pulse including two rising edges and two trailing edges has a maximum value, an intermediate value and a minimum value. Thus, the inventor of the present invention found that calculation of plus values and minus values could be easily performed by regarding the intermediate value as zero. In case of performing calculation with using the conventional pulse waves, setting a complement number for minus values is required. On the other hand, in case of using the step-like pulse waves, minus values can be directly calculated.